1. Field of the Invention
The present invention relates to a heat radiation shield coating composition which can be applied onto roofs and outside walls of architectural structures, vehicles, ships, plants, sheds, cattle stalls and the like.
2. Description of Related Art
Coatings are applied onto various structures, such as roofs of architectural structures, to impart various color appearances thereto. However, carbon black, a typical black pigment for use in production of various color hues, tends to absorb a solar energy. This nature inevitably leads to elevation in temperature inside a structure having a coat formed from a carbon black containing composition, which impairs comfort of residential spaces and storage conditions of articles and also requires a huge energy consumption for air conditioning.
In Japanese Patent Laying-Open Nos. Hei 1-121371 (1989) and Hei 1-261466 (1989), the use of various metal oxide or mixed metal oxide pigments is disclosed for solar radiation shield pigments. Still, the use of conventional carbon black is necessary to obtain a coating that exhibits a high level of blackness, resulting in the reduced heat radiation shielding effect. Japanese Patent Laying-Open No. Hei 2-185572 (1990) proposes the use of a mixed oxide black pigment. This pigment however exhibits a solar radiation reflectance of below 8% and thus its heat radiation shielding effect is limited.
Japanese Patent Registration No. 2593968 and Japanese Patent Laying-Open No. Hei 05-293434 (1993) propose solar heat shield coating compositions colored in an achromatic black by blending chromatic pigments, such as red, orange, yellow, green, blue and purple pigments which exhibit high solar radiation reflectances in the ultraviolet and near infrared regions. However, prolonged use thereof likely results in problematic partial deterioration of those color pigments. This unbalances the initial color matching to cause a color change, which has been a problem.
It is an object of the present invention to provide a heat radiation shield coating composition containing a black pigment, which can form a coating film having a superior heat radiation shielding capability.
The heat radiation shield coating composition of the present invention contains a black pigment that exhibits a reflectance of not below 8.0% relative to a solar radiation in the 780-2,100 nm wavelength region.
Preferably, the black pigment exhibits a reflectance of not exceeding 15% to a radiation at any wavelength within the 400-700 nm visible region.
The black pigment may be a calcined pigment containing Fe2O3 and also Cr2O3 and/or Mn2O3 in the total amount of 20-100% by weight.
The heat radiation shield coating composition may contain the above-specified black pigment in the amount of not below 0.1% by weight. Preferably, the black pigment accounts for at least 0.5% of the total weight of all pigments.
The heat radiation shield coating composition may preferably contain, as a binder component, a polyester, acrylic, fluoro or chloro resin. It may further contain a melamine resin and/or blocked isocyanate, when needed. A heat radiation shielding plate of this invention is a plate coated with the above-specified heat radiation shield coating composition.
As stated above, the heat radiation shield coating composition of the present invention contains a black pigment that exhibits a reflectance of not below 8.0% relative to a solar radiation in the 780-2,100 nm wavelength region.
The black pigment for use in the heat radiation shield coating composition exhibits a reflectance of not below 8%, preferably not below 15.0%, relative to a solar radiation. The solar radiation reflectance, as used herein, is described in JIS A 5759 and is defined therein as the solar radiation reflectance weighted by an intensity of a solar radiation at each wavelength in the 780-2,100 nm region. If the solar radiation reflectance is below 8.0%, sufficient heat radiation shielding characteristics may not be obtained. Accordingly, in the case where a coating composition containing such a black pigment is utilized to provide coatings on roofs and outside walls of architectural structures, vehicles, ships, plants, sheds, cattle stalls and the like, such coatings may fail to achieve sufficient reduction of temperature inside those structures.
The black pigment, as used herein, refers to a pigment that has a blackxe2x80x94dark brown appearance.
Preferably, the black pigment with the above-specified solar radiation reflectance is a calcined inorganic pigment which contains Fe2O3 and also Cr2O3 and/or Mn2O3 in the total amount of 20-100% by weight. Specifically, this calcined pigment is characterized as containing Fe2O3, as an essential ingredient, and also at least one of Cr2O3 and Mn2O3. These ingredients are preferably contained in the calcined pigment in the total amount of 20-100% by weight, more preferably of 30-100% by weight. If the total amount is below 20% by weight, the calcined pigment may exhibit an insufficient heat radiation shielding capability.
The above-described calcined pigment is generally manufactured via calcination at a temperature of at least 600xc2x0 C. and the subsequent pulverization.
The heat radiation shield coating composition of the present invention contains the black pigment as an essential component, but may further contain other color, body or bright pigment depending upon the color hue, end purpose and performance sought for the resulting coating. In such a case, the coating composition preferably contains the black pigment in the amount of at least 0.1% by weight. If the amount is below 0.1% by weight, it may fail to exhibit a sufficient heat radiation shielding performance. Also, the black pigment preferably accounts for at least 0.5% of the total weight of all pigment components. With the higher loading thereof, the resulting coating can exhibit the increased heat radiation shielding capability compared to conventional coatings of the same color hue. If the proportion by weight of the black pigment is reduced to below 0.5%, the resulting coating with the same hue may fail to exhibit a sufficient heat radiation shielding performance.
As stated above, the heat radiation shield coating composition of the present invention may further contain other color pigment than the black pigment or other type of pigment such as a body or bright pigment.
The other color pigment is used to adjust a hue of a coating and may be an organic or inorganic color pigment. Examples of organic color pigments include phthalocyanine, azo, condensed azo, anthraquinone, perinone/perylene, indigo/thioindigo, isoindolinone, azomethineazo, dioxazine, quinacridone, aniline black, triphenylmethane pigments and the like. Examples of inorganic color pigments include titanium oxide, iron oxide, iron hydroxide, chrome oxide, calcined spinel pigments, lead chromate, chrome vermilion, iron blue pigments, aluminum powder, bronze powder and the like.
Examples of body pigments include calcium carbonate, barium sulfate, silicon oxide, aluminum hydroxide and the like. Other applicable body pigments include organic cross-linked particles and inorganic particles.
Examples of bright pigments include a mica pigment, an aluminum foil, a tin foil, a gold leaf, a stainless steel foil and a metal foil pigment such as of nickel, copper or the like.
The type and form of the heat radiation shield coating composition of the present invention is not particularly specified. Its type can be thermosetting, thermoplastic, ambient drying, ambient curable or radiation curable. It can be provided in a solvent-borne, water-borne, non-aqueous emulsion, solvent-free or powder form.
The coating composition of the present invention may also contain a binder component, examples of which include acrylic, alkyd, polyester, silicone-modified polyester, silicone-modified acrylic, epoxy, polycarbonate, silicate, fluoro and chloro resins. The use of a polyester, acrylic, fluoro or chloro resin, among those resins, is preferred.
When necessary, the coating composition may further contain a curing agent, examples of which include amino resins such as a melamine resin and crosslinking resins such as isocyanate and blocked isocyanate.
The heat radiation shield coating composition of the present invention may further contain a filler consisting of fine particles, an additive, a solvent and the like, when needed.
The type of the filler is not particularly specified. Examples of fillers include fine particles composed of SiO2, TiO2, Al2O3, Cr2O3, ZrO2, Al2O3.SiO2, 3Al2O3.2SiO2, zirconia silicate or the like; finely divided fibrous or particulate glass and the like.
The type of the additive is not particularly specified. Useful additives are conventionally known in the art and include, for example, a flatting agent such as silica or alumina, defoamer, leveling agent, antisagging agent, surface control agent, viscosity control agent, dispersing agent, UV absorber, wax and the like.
Any type of solvent generally known to be useful for coatings can be used. Examples of solvents include aromatic hydrocarbons such as toluene, xylene, SOLVESSO 100 and SOLVESSO 150; esters such as ethyl acetate and butyl acetate; ketones such as methylethyl ketone, methylisobutyl ketone, cyclohexanone and isophorone; and water. The solvent used is suitably chosen from those listed above on the basis of solubility, evaporation rate and safety considerations. The above-listed solvents may be used alone or in any combination thereof.
The heat radiation shield coating composition contains the black pigment having the above-specified solar radiation reflectance under the consideration of a solar radiation intensity at each wavelength. It effectively reflects a near infrared radiation in the 780-2,100 nm wavelength region, which constitutes a primary heat source of a solar radiation. The composition thus becomes particularly effective when used to form a solar radiation shield coating film.
The following procedure can be utilized to prepare the coating composition of the present invention. The above-described black pigment is mixed in a pigment dispersing resin by means of a machinery generally used in the art to disperse pigments, such as a roller mill, paint shaker, pot mill, disper or sand grinding mill, to prepare a pigment-dispersed paste. The above-described binder, melamine resin and/or blocked isocyanate, additive, solvent and others are then added to the paste to provide a coating composition.
Various coating techniques and equipments generally known in the art can be utilized to apply the present coating composition, including dipping, brushing, a roller, a roll coater, an air spray, an airless spray, a curtain flow coater, a roller curtain coater, die coater and the like, for example. The coating technique may be suitably chosen depending upon the end purpose of the substrate used.
The heat radiation shielding plate of the present invention is the plate having a coating film formed from the coating composition of the present invention. The coating film formed thereon may be varied in thickness depending on the type and end use of the coating composition used, but has a dry thickness generally in the range of 5-300 xcexcm.
The material type of a substrate to which the heat radiation shield coating composition of the present invention can be applied is not particularly limited, and include, for example, metals, plastics, inorganics and the like. Examples of metals include aluminum, iron, zinc plated steel, aluminum-zinc plated steel, stainless steel, tin and the like. Examples of plastics include acrylics, vinyl chloride, polycarbonates, ABS, polyethylene terephthalate, polyolefins and the like. Examples of inorganics include ceramics such as referred to in JIS A 5422 and A 5430, glass and the like.
The above-listed substrates may be surface treated to impart improved adhrerence or corrosion resistance thereto. Further, an undercoat may be applied thereover. Still further, a back coat may be applied over a back surface of the substrate.